[llvm-exegesis] Add throughput mode.

[courbet]

Summary

This just uses the latency benchmark runner on the parallel uops snippet
generator.

Fixes PR37698.

[courbet]

fix typo

docs/CommandGuide/llvm-exegesis.rst

 llvm-exegesis - LLVM Machine Instruction Benchmark
 ==================================================
 
 SYNOPSIS
 --------
 
 :program:`llvm-exegesis` [*options*]
 
 DESCRIPTION
 -----------
 
 :program:`llvm-exegesis` is a benchmarking tool that uses information available
-in LLVM to measure host machine instruction characteristics like latency or port
-decomposition.
+in LLVM to measure host machine instruction characteristics like latency,
+thoughput, or port decomposition.
 
 Given an LLVM opcode name and a benchmarking mode, :program:`llvm-exegesis`
 generates a code snippet that makes execution as serial (resp. as parallel) as
-possible so that we can measure the latency (resp. uop decomposition) of the
-instruction.
+possible so that we can measure the latency (resp. inverse throughput/uop decomposition)
+of the instruction.
 The code snippet is jitted and executed on the host subtarget. The time taken
 (resp. resource usage) is measured using hardware performance counters. The
 result is printed out as YAML to the standard output.
 
 The main goal of this tool is to automatically (in)validate the LLVM's TableDef
 scheduling models. To that end, we also provide analysis of the results.
 
 :program:`llvm-exegesis` can also benchmark arbitrary user-provided code
 snippets.
 
 EXAMPLE 1: benchmarking instructions
 ------------------------------------
 
 Assume you have an X86-64 machine. To measure the latency of a single
 instruction, run:
 
 .. code-block:: bash
 
     $ llvm-exegesis -mode=latency -opcode-name=ADD64rr
 
-Measuring the uop decomposition of an instruction works similarly:
+Measuring the uop decomposition or inverse throughput of an instruction works similarly:
 
 .. code-block:: bash
 
     $ llvm-exegesis -mode=uops -opcode-name=ADD64rr
+    $ llvm-exegesis -mode=inverse_throughput -opcode-name=ADD64rr
+
 
 The output is a YAML document (the default is to write to stdout, but you can
 redirect the output to a file using `-benchmarks-file`):
 
 .. code-block:: none
 
   ---
   key:

  a comma-separated list. See example 1 for details.
  Either `opcode-index`, `opcode-name` or `snippets-file` must be set.
 
  .. option:: -snippets-file=<filename>
 
   Specify the custom code snippet to measure. See example 2 for details.
   Either `opcode-index`, `opcode-name` or `snippets-file` must be set.
 
-.. option:: -mode=[latency|uops|analysis]
+.. option:: -mode=[latency|uops|inverse_throughput|analysis]
 
  Specify the run mode.
 
 .. option:: -num-repetitions=<Number of repetition>
 
  Specify the number of repetitions of the asm snippet.
  Higher values lead to more accurate measurements but lengthen the benchmark.
 
 .. option:: -benchmarks-file=</path/to/file>
 
- File to read (`analysis` mode) or write (`latency`/`uops` modes) benchmark
- results. "-" uses stdin/stdout.
+ File to read (`analysis` mode) or write (`latency`/`uops`/`inverse_throughput`
+ modes) benchmark results. "-" uses stdin/stdout.
 
 .. option:: -analysis-clusters-output-file=</path/to/file>
 
  If provided, write the analysis clusters as CSV to this file. "-" prints to
  stdout.
 
 .. option:: -analysis-inconsistencies-output-file=</path/to/file>
 

test/tools/llvm-exegesis/X86/inverse_throughput-by-opcode-name.s

+# RUN: llvm-exegesis -mode=inverse_throughput -opcode-name=ADD32rr | FileCheck %s
+
+CHECK:      ---
+CHECK-NEXT: mode: inverse_throughput
+CHECK-NEXT: key:
+CHECK-NEXT:   instructions:
+CHECK-NEXT:     ADD32rr
+CHECK: key: inverse_throughput

tools/llvm-exegesis/lib/BenchmarkResult.h

struct BenchmarkMeasure {
   // This is the per-snippet value, i.e. measured quantity for one repetition of
   // the whole snippet.
   double PerSnippetValue;
 };
 
 // The result of an instruction benchmark.
 struct InstructionBenchmark {
   InstructionBenchmarkKey Key;
-  enum ModeE { Unknown, Latency, Uops };
+  enum ModeE { Unknown, Latency, Uops, InverseThroughput };
   ModeE Mode;
   std::string CpuName;
   std::string LLVMTriple;
   // The number of instructions inside the repeated snippet. For example, if a
   // snippet of 3 instructions is repeated 4 times, this is 12.
   int NumRepetitions = 0;
   // Note that measurements are per instruction.
   std::vector<BenchmarkMeasure> Measurements;

tools/llvm-exegesis/lib/BenchmarkResult.cpp

 
 template <>
 struct ScalarEnumerationTraits<exegesis::InstructionBenchmark::ModeE> {
   static void enumeration(IO &Io,
                           exegesis::InstructionBenchmark::ModeE &Value) {
     Io.enumCase(Value, "", exegesis::InstructionBenchmark::Unknown);
     Io.enumCase(Value, "latency", exegesis::InstructionBenchmark::Latency);
     Io.enumCase(Value, "uops", exegesis::InstructionBenchmark::Uops);
+    Io.enumCase(Value, "inverse_throughput",
+                exegesis::InstructionBenchmark::InverseThroughput);
   }
 };
 
 // std::vector<exegesis::RegisterValue> will be rendered as a list.
 template <> struct SequenceElementTraits<exegesis::RegisterValue> {
   static const bool flow = false;
 };
 

tools/llvm-exegesis/lib/BenchmarkRunner.h

public:
   public:
     virtual ~FunctionExecutor();
     virtual llvm::Expected<int64_t>
     runAndMeasure(const char *Counters) const = 0;
   };
 
 protected:
   const LLVMState &State;
+  const InstructionBenchmark::ModeE Mode;
 
 private:
   virtual llvm::Expected<std::vector<BenchmarkMeasure>>
   runMeasurements(const FunctionExecutor &Executor) const = 0;
 
   llvm::Expected<std::string>
   writeObjectFile(const BenchmarkCode &Configuration,
                   llvm::ArrayRef<llvm::MCInst> Code) const;
 
-  const InstructionBenchmark::ModeE Mode;
 
   const std::unique_ptr<ScratchSpace> Scratch;
 };
 
 } // namespace exegesis
 } // namespace llvm
 
 #endif // LLVM_TOOLS_LLVM_EXEGESIS_BENCHMARKRUNNER_H

tools/llvm-exegesis/lib/Latency.h

public:
   ~LatencySnippetGenerator() override;
 
   llvm::Expected<std::vector<CodeTemplate>>
   generateCodeTemplates(const Instruction &Instr) const override;
 };
 
 class LatencyBenchmarkRunner : public BenchmarkRunner {
 public:
-  LatencyBenchmarkRunner(const LLVMState &State)
-      : BenchmarkRunner(State, InstructionBenchmark::Latency) {}
+  LatencyBenchmarkRunner(const LLVMState &State,
+                         InstructionBenchmark::ModeE Mode);
   ~LatencyBenchmarkRunner() override;
 
 private:
   llvm::Expected<std::vector<BenchmarkMeasure>>
   runMeasurements(const FunctionExecutor &Executor) const override;
 };
 } // namespace exegesis
 } // namespace llvm
 
 #endif // LLVM_TOOLS_LLVM_EXEGESIS_LATENCY_H

tools/llvm-exegesis/lib/Latency.cpp

if (!Results.empty())
       break;
   }
   if (Results.empty())
     return llvm::make_error<BenchmarkFailure>(
         "No strategy found to make the execution serial");
   return std::move(Results);
 }
 
+LatencyBenchmarkRunner::LatencyBenchmarkRunner(const LLVMState &State,
+                                               InstructionBenchmark::ModeE Mode)
+    : BenchmarkRunner(State, Mode) {
+  assert((Mode == InstructionBenchmark::Latency ||
+          Mode == InstructionBenchmark::InverseThroughput) &&
+         "invalid mode");
+}
+
 LatencyBenchmarkRunner::~LatencyBenchmarkRunner() = default;
 
 llvm::Expected<std::vector<BenchmarkMeasure>>
 LatencyBenchmarkRunner::runMeasurements(
     const FunctionExecutor &Executor) const {
   // Cycle measurements include some overhead from the kernel. Repeat the
   // measure several times and take the minimum value.
   constexpr const int NumMeasurements = 30;
   int64_t MinValue = std::numeric_limits<int64_t>::max();
   const char *CounterName = State.getPfmCounters().CycleCounter;
   if (!CounterName)
     llvm::report_fatal_error("sched model does not define a cycle counter");
   for (size_t I = 0; I < NumMeasurements; ++I) {
     auto ExpectedCounterValue = Executor.runAndMeasure(CounterName);
     if (!ExpectedCounterValue)
       return ExpectedCounterValue.takeError();
     if (*ExpectedCounterValue < MinValue)
       MinValue = *ExpectedCounterValue;
   }
-  std::vector<BenchmarkMeasure> Result = {
-      BenchmarkMeasure::Create("latency", MinValue)};
+  std::vector<BenchmarkMeasure> Result;
+  switch (Mode) {
+  case InstructionBenchmark::Latency:
+    Result = {BenchmarkMeasure::Create("latency", MinValue)};
+    break;
+  case InstructionBenchmark::InverseThroughput:
+    Result = {BenchmarkMeasure::Create("inverse_throughput", MinValue)};
+    break;
+  default:
+    break;
+  }
   return std::move(Result);
 }
 
 } // namespace exegesis
 } // namespace llvm

tools/llvm-exegesis/lib/Target.h

private:
 
   // Targets can implement their own snippet generators/benchmarks runners by
   // implementing these.
   std::unique_ptr<SnippetGenerator> virtual createLatencySnippetGenerator(
       const LLVMState &State) const;
   std::unique_ptr<SnippetGenerator> virtual createUopsSnippetGenerator(
       const LLVMState &State) const;
   std::unique_ptr<BenchmarkRunner> virtual createLatencyBenchmarkRunner(
-      const LLVMState &State) const;
+      const LLVMState &State, InstructionBenchmark::ModeE Mode) const;
   std::unique_ptr<BenchmarkRunner> virtual createUopsBenchmarkRunner(
       const LLVMState &State) const;
 
   const ExegesisTarget *Next = nullptr;
   const llvm::ArrayRef<CpuAndPfmCounters> CpuPfmCounters;
 };
 
 } // namespace exegesis
 } // namespace llvm
 
 #endif // LLVM_TOOLS_LLVM_EXEGESIS_TARGET_H

tools/llvm-exegesis/lib/Target.cpp

 ExegesisTarget::createSnippetGenerator(InstructionBenchmark::ModeE Mode,
                                        const LLVMState &State) const {
   switch (Mode) {
   case InstructionBenchmark::Unknown:
     return nullptr;
   case InstructionBenchmark::Latency:
     return createLatencySnippetGenerator(State);
   case InstructionBenchmark::Uops:
+  case InstructionBenchmark::InverseThroughput:
     return createUopsSnippetGenerator(State);
   }
   return nullptr;
 }
 
 std::unique_ptr<BenchmarkRunner>
 ExegesisTarget::createBenchmarkRunner(InstructionBenchmark::ModeE Mode,
                                       const LLVMState &State) const {
   switch (Mode) {
   case InstructionBenchmark::Unknown:
     return nullptr;
   case InstructionBenchmark::Latency:
-    return createLatencyBenchmarkRunner(State);
+  case InstructionBenchmark::InverseThroughput:
+    return createLatencyBenchmarkRunner(State, Mode);
   case InstructionBenchmark::Uops:
     return createUopsBenchmarkRunner(State);
   }
   return nullptr;
 }
 
 std::unique_ptr<SnippetGenerator>
 ExegesisTarget::createLatencySnippetGenerator(const LLVMState &State) const {
   return llvm::make_unique<LatencySnippetGenerator>(State);
 }
 
 std::unique_ptr<SnippetGenerator>
 ExegesisTarget::createUopsSnippetGenerator(const LLVMState &State) const {
   return llvm::make_unique<UopsSnippetGenerator>(State);
 }
 
-std::unique_ptr<BenchmarkRunner>
-ExegesisTarget::createLatencyBenchmarkRunner(const LLVMState &State) const {
-  return llvm::make_unique<LatencyBenchmarkRunner>(State);
+std::unique_ptr<BenchmarkRunner> ExegesisTarget::createLatencyBenchmarkRunner(
+    const LLVMState &State, InstructionBenchmark::ModeE Mode) const {
+  return llvm::make_unique<LatencyBenchmarkRunner>(State, Mode);
 }
 
 std::unique_ptr<BenchmarkRunner>
 ExegesisTarget::createUopsBenchmarkRunner(const LLVMState &State) const {
   return llvm::make_unique<UopsBenchmarkRunner>(State);
 }
 
 static_assert(std::is_pod<PfmCountersInfo>::value,

tools/llvm-exegesis/llvm-exegesis.cpp

 
 static cl::opt<std::string> SnippetsFile("snippets-file",
                                          cl::desc("code snippets to measure"),
                                          cl::init(""));
 
 static cl::opt<std::string> BenchmarkFile("benchmarks-file", cl::desc(""),
                                           cl::init(""));
 
-static cl::opt<exegesis::InstructionBenchmark::ModeE>
-    BenchmarkMode("mode", cl::desc("the mode to run"),
-                  cl::values(clEnumValN(exegesis::InstructionBenchmark::Latency,
-                                        "latency", "Instruction Latency"),
-                             clEnumValN(exegesis::InstructionBenchmark::Uops,
-                                        "uops", "Uop Decomposition"),
-                             // When not asking for a specific benchmark mode,
-                             // we'll analyse the results.
-                             clEnumValN(exegesis::InstructionBenchmark::Unknown,
-                                        "analysis", "Analysis")));
+static cl::opt<exegesis::InstructionBenchmark::ModeE> BenchmarkMode(
+    "mode", cl::desc("the mode to run"),
+    cl::values(clEnumValN(exegesis::InstructionBenchmark::Latency, "latency",
+                          "Instruction Latency"),
+               clEnumValN(exegesis::InstructionBenchmark::InverseThroughput,
+                          "inverse_throughput",
+                          "Instruction Inverse Throughput"),
+               clEnumValN(exegesis::InstructionBenchmark::Uops, "uops",
+                          "Uop Decomposition"),
+               clEnumValN(exegesis::InstructionBenchmark::Unknown, "analysis",
+                          "Analysis")));
 
 static cl::opt<unsigned>
     NumRepetitions("num-repetitions",
                    cl::desc("number of time to repeat the asm snippet"),
                    cl::init(10000));
 
 static cl::opt<bool> IgnoreInvalidSchedClass(
     "ignore-invalid-sched-class",